1. Field of the Invention
The present invention relates to a method for forming a thin film, such as vacuum deposition, sputtering and chemical vapor deposition, and an apparatus therefor.
2. Prior Art
Recently, devices manufactured with thin film techniques have been researched by many workers in order to add functions and value thereto, and thin film process technology on which the characteristics of the devices depend has become an important key technology. The characteristics of thin films are affected largely by the material, shape and the like of substrates to which the thin films are applied. Therefore, individual techniques for manufacturing thin films are necessary for each usage and for each object.
When a thin film is formed on the surface of a three dimensional substrate, a film is deposited, for example, while the substrate is rotated so as to expose the surface of the substrate and allow a uniform film to be deposited. There is known a type of prior art thin film forming apparatus exemplified as an ion plating apparatus disclosed in Japanese Utility Model laid open Publication 57955/1990 and a barrel coating apparatus disclosed in Japanese Patent laid open Publication 125869/1990. In the former ion plating apparatus, many substrates are attached to a holder, and the substrates are revolved with rotation of the holder. Then, a uniform thin film is formed on each substrate. In the latter barrel coating apparatus, many substrates are enclosed in a rotating tubular barrel and evaporation material is supplied from a crucible arranged inside the barrel.
However, in such prior art apparatuses, the precision of the size of substrates to which a thin film is applied becomes deteriorated in the process of manufacturing the thin film if the substrate is a component to be used in a precision mechanism and high mechanical precision is required. Further, a problem of mass productivity may arise, depending on the form of the substrate.
For example, in an apparatus wherein a substrate such as a capstan shaft for a videocassette recorder which must be manufactured precisely has to be held in a holder, stress may arise and strain due to the stress may be generated when the temperature increases in the film-forming process. In an apparatus wherein substrates are included in a barrel, a thin film is also adhered on the barrel, and this undesirable film causes many problems. For example, if the material of the film has high electrical resistance, the quality of film becomes lower. For example, the potential of the substrate becomes unstable or discharge may cause damage to the substrate. Further, the thermal conduction from the substrate to the barrel is hindered by the film and the temperature of the substrate becomes high.